As far as i am aware the Installer must carry out a RISK ASSESSMENT, and if there is any danger of the pipes being at risk of damage or dislocation, then the installer must take steps to ensure that all practicable steps are taken to minimise this. Commercially, we normally get round this by installing screwed steel pipes - albeit domestically this is less utilised and boxing is employed if there is a proven hazzard. Ultimately, if you are concerned by the installation you can insist the installer sends you a copy of the risk assessment, to which you are entitled, and can seek a second opinion.